The prior art includes a wide variety of devices which generally fall into the broad category of pressure transducers. Certain of these transducers exhibit a change in resistance as a function of an applied force or pressure. Another class of pressure transducers employ a variation of capacitance to determine the magnitude of an applied force. These devices operate to vary the capacitance between a movable plate and a stationary plate. The movable plate is a flexible diaphragm which will deflect upon application of a suitable force by an amount proportional to the force. The motion of the plate serves to vary the effective distance between the movable plate and the fixed plate. As is well known, the distance between two parallel plates determines the magnitude of the effective capacitance. In conjunction with such capacitance variation one can also use an inductor and therefore provide an LC circuit whereby the resonant frequency of the circuit changes as a function of capacitance. A particular device according to this principle is depicted in U.S. Pat. No. 6,891,711. This patent issued on May 10, 2005, to A. D. Kurtz, one of the inventors herein, and is assigned to Kulite Semiconductor Products, Inc., the assignee herein. The patent is entitled “Ultra-Miniature High Temperature Capacitive Inductive Pressure Transducer”. In that patent the capacitive inductive pressure transducer is fabricated by MEMS techniques. The transducer consists of two separated pieces of silicon which form the plates of the capacitor, one of which plate is micro-machined in such a way as to allow a deflection with pressure. The gap between the two capacitive plates is determined by an extending rim on one of the two plates. The two pieces of silicon are subsequently fusion bonded, leading to a very small gap between the two plates. An inductor is formed on the top surface of one of the pieces of silicon by sputtering metal in a spiral-like fashion on the back side of the non-micro-machined plate. The above noted patent describes in detail a device which essentially is a capacitive inductive transducer. As one can ascertain the device in the above noted patent is fabricated from silicon and has a limited temperature operation because of the component structure of the device. In any event, there are pressure transducers which operate at extremely high temperatures and are fabricated from silicon carbide. See, for example, U.S. Pat. No. 6,691,581 issued on Feb. 17, 2004, entitled “Pressure Transducer Fabricated from Beta Silicon Carbide” by A. D. Kurtz et al and assigned to the assignee herein. That patent shows a method of fabricating a dielectrically isolated silicon carbide high temperature transducer, which is capable of operating at temperatures above 600° C. See also, U.S. Pat. No. 6,327,911 issued on Dec. 11, 2001 entitled “High Temperature Pressure Transducer Fabricated From Beta Silicon Carbide” issued on Dec. 11, 2001 to A. D. Kurtz et al and assigned to the assignee herein. That patent shows a high temperature pressure transducer which employs silicon carbide as a sensing element or sensor which sensors are situated on a diaphragm also fabricated from silicon carbide. The dielectrically isolated pressure sensing elements are formed on the diagram by a method which employs two separately fabricated wafers that are later bonded together. As one can ascertain the above noted patents depict pressure transducers which are fabricated from beta silicon carbide and which operate at extremely high temperatures. The reason for replacing the silicon as used in U.S. Pat. No. 6,891,711 with silicon carbide or aluminum nitride is to permit the operation of the pressure transducer at significantly higher temperatures. At approximately 600° to 700° C. silicon deforms plastically under high stresses, thus rendering such devices inoperable. For silicon carbide and aluminum nitride the temperatures at which deformation will occur is in excess of 1500° C.
Thus, there is described a method for fabricating an LC circuit utilizing silicon carbide and therefore enabling the device to operate at extremely high temperatures.